Why did you post this? The article is nonsense and it's main point is based on an incomplete and incorrect reading of the BLS definition of what is and is not a bicycle messenger. Non-food bicycle courier service is dead outside of a few niche businesses located only in the largest american urban cores.
US BLS does not specifically sign bicycle messengers:
Pick up and deliver messages, documents, packages, and other items between offices or departments within an establishment or directly to other business concerns, traveling by foot, bicycle, motorcycle, automobile, or public conveyance. Excludes "Light Truck or Delivery Services Drivers"
https://www.bls.gov/oes/current/oes435021.htm
From the article:
According to the USDOL there were 138,000 messengers in 1996, 120,000 messengers in 1998, 141,000 messengers in 2000 (although the classification changed so comparison to prior years is unreliable.)
You can't seriously believe there were ever this many bicycle messengers employed in the USA?